MIP (Mobile IP) is a protocol that was originally proposed by the IETF (Internet Engineering Task Force) and is described in “RFC 2002—IP Mobility Support”. In a MIP network, a HA (home agent) typically assigns a static home IP address to each associated mobile device. As a mobile device roams in the MIP network, it registers with a FA (foreign agent), which provides a COA (care-of-address). The HA is informed of the mobile device's COA through the registration procedure. The FA maintains a binding of the home IP address to COA for a certain length of time called a registration lifetime. A tunnel is established between the HA and the mobile device enabling the HA to send packets to the mobile device by means of the FA; therefore, the mobile device is reachable via its home IP address. As long as the mobile device re-registers before the registration lifetime expires, a PPP (point to point protocol) connectivity is maintained.
In a SIP (Simple IP) network, mobile devices are assigned geographically dependent IP addresses dynamically by a visited PDSN (Packet Data Serving Nodes). As the mobile device roams it will be assigned a new geographically dependent IP address for a duration that may not be known to the mobile device. MIP provides a number of advantages over SIP (Simple IP) such as enabling communication with the mobile device using its non-geographically dependent home IP address. The elimination of the need to know the mobile device's current geographical point of attachment greatly enhances roaming capabilities and enables different application servers to reach the mobile device via its known home IP address regardless of its current point of attachment to the MIP network. Also, MIP enables multiple user profiles with different user ID/password etc.
A mobile device that is configured as “Mobile IP only” may encounter a number of registration issues in a network—both in home and in roaming. If such situations are not handled properly, then it may lead to disruption in data connectivity resulting in a poor user experience in case of an “always-on” mobile device. On the other hand, brute force retry attempts by the mobile device to re-register with the MIP network can cause unwarranted MIP network access, a reduced battery life of the mobile device, and congestion of the MIP network.